Physiological electrodes attached to the skin of a subject can receive electrical signals generated by the human body, which are then used to monitor physiological functions (such as heart rate and muscle activity), and/or can deliver electrical signals to the body, for example to stimulate muscle contraction or relieve pain.
For example, transcutaneous electrical nerve stimulation (TENS) is a technique in which electric current is applied to a body part of the subject via two or more skin mounted electrodes. TENS treatment typically requires electrical current to be applied to the body for a significant amount of time each day, including while the subject goes about their daily activities. In wireless TENS, a TENS device (which generates the electrical current in response to a signal from a control unit) is placed directly on an electrode attached to the skin of a subject. FIG. 1 shows a wireless TENS system comprising a TENS device 10 carried by two electrodes 12, 14, and a remote control 16, being used to treat the lower back of a subject 18.
It is a key benefit for a user of a TENS or other electrode-based system to be able to easily connect and disconnect the medical device from the electrode. This facilitates connection to electrodes in difficult to reach body positions (e.g. the back) and on soft tissue areas which do not offer much resistance to a pushing or pulling force. An easy-to-use connector is also necessary for subjects who have reduced use of their hands and fingers (for example because they suffer from osteoarthritis).
Known skin electrodes, including those used for TENS, are typically connected to a medical device (such as a TENS device) using a mechanical connection. One known type of electrode has a lead wire which extends from the top surface of the electrode pad and ends in a female jack connector. This is configured to engage in a push-fit connection with a male jack connector provided on a lead wire extending from a medical device.
Another commonly-used type of electrode 20, shown in FIG. 2a, has a male snap structure 22 configured to engage in a snap-fit connection with a female receiving portion 24 of a medical device connector 26 (shown in FIG. 2b). The snap connection is achieved by cooperation between the shape of the male snap structure 22 and the shape of the female receiving portion 24. In the illustrated example, a metal spring 28 on the receiving portion 24 seats into a recessed portion of male snap structure 22 when the electrode 20 and connector 26 are connected.
The mechanical connection between the male and female structures of the snap connector means that force is required to connect and disconnect the electrodes from the medical device. This makes such connectors difficult to use by people who are unable to easily apply the required amount of force. It also makes connection to electrodes located on soft body parts (such as the stomach) very difficult or impossible, since such body parts do not provide a firm support to press or pull against. It also makes connection to electrodes located on painful body parts (for example which have been injured) unpleasant; since the force which needs to be applied may cause further pain and discomfort. These difficulties of connecting the medical device connector and the electrode may lead to improper connections, reducing the effectiveness of the treatment or monitoring being carried out by means of the medical device.
To mitigate these issues, the use of magnetic connectors to connect medical devices to electrodes has been proposed. WO2011/151742, for example, describes an electrode assembly comprising an electrode and a connector, in which a connection between the electrode and connector is formed by way of a magnet provided in the connector assembly magnetically coupling to a magnet or portion of ferromagnetic material in the electrode.
An example of a magnetic connector/electrode assembly is shown in FIG. 3a. The illustrated medical device 10 has a connector 32 comprising an annular magnet 34. It is connected to an electrode 30 having a circular ferromagnetic metal target 36. The target 36 has a central stud 38 which engages the hole in the annular magnet 34. The cooperation between the stud 38 and the hole prevents relative lateral movement of the electrode 30 and the medical device 10, but does not hinder their separation. Another example of a known magnetic connector/electrode assembly is shown in FIG. 3b. In this example the medical device 10 has a connector 33 which comprises a magnet 35 which protrudes from an outer surface of the medical device 11. It is connected to an electrode 31 having a ferromagnetic metal target 37 with a central recess configured to receive the magnet 35, so that lateral movement between the electrode 31 and the medical device 11 is prevented.
Since electrodes which must be adhered to a patient's skin are typically used just once, or a few times, before being disposed of, TENS patients and medical facilities which make use of electrode-based medical devices must periodically purchase stocks of electrodes. If a patient or medical facility acquires a new medical device which uses a different type of connector, for example a magnetic connector, they also need to purchase a new stock of specialised electrodes adapted for use with this particular type of connector. If they no longer have any devices using the old type of connector, they will also have to discard any remaining of their existing stock of electrodes.
It would therefore be desirable to be able to use conventional, mechanical-connector type electrodes with medical devices that use magnetic connectors, so that the above-described benefits of magnetic connectors can be obtained without the expense of purchasing new stocks of electrodes, or, in the case of a medical facility which uses various types of electrode-based medical devices, the inconvenience of having to maintain stocks of several different types of electrode.